1. Field of the Invention
The present invention relates to structural composites, and more particularly to structural composites which bear indicia or designs. Even more particularly, the present invention relates to an article of composite material and a method of making the same in which the article exhibits one or more surface regions bearing indicia or design information which has been applied through a sublimation printing process.
2. Description of the Related Art
The fabrication of structural composite elements, and assemblies made from such elements, to obtain increased strength-to-weight characteristics and other improved properties is well known. Such elements typically are comprised of high strength fibers embedded in a polymer resin matrix. In a similar manner, assemblies of composite materials are made from layers of such elements embedded in a polymer resin. The typical process for forming a composite structure entails building a stack of layers or plies of composite material and embedding the entire stack in the polymer resin matrix. In this situation, each ply can be the same or different material and the fibers in each ply can be wrapped with different braiding patterns to satisfy pre-specified requirements of a particular structure.
The processes and the apparatus for the fabrication of such composite elements and assemblies are well known to persons of ordinary skill in that art. The processes include pultrulsion and resin transfer molding, and the fiber materials, which have included aramid, kevlar, glass, carbon, graphite, ceramics and a variety of metals, are immersed in a polymer matrix material. Typically, the polymer matrix material is a thermoset resin such as polyester or epoxy resin, or it can be a thermoplastic resin such as nylon, polypropylene, polycarbonate, etc.
Sublimation printing is a process that has long been known for the purpose of imprinting indicia (alphanumeric data, designs, logos, etc) onto an article. Generally, sublimation is a direct transformation from a solid state to a vapour state, and special sublimable inks, prepared on articles, such as sheets of fabric, paper or the like, transfer by sublimation from the sheets to the articles to be printed or decorated when the sheets are held adjacent to the articles and then heated.
Sublimation printing or decoration has many advantages compared to other decoration processes. In fact, in sublimation printing, vapors of the ink penetrate the article being printed and generate vivid and very pleasant, decorations of virtually no thickness.
The best results are achieved with some plastic materials for the penetration in those plastic materials of sublimable inks, but it is well known that nearly all materials may be sublimation-printed if a an adherent paint layer is previously applied on the same. For example,
Sublimation printing of substantially flat articles is easily realizable and is generally carried out with hot presses or irons, which press sublimable ink-bearing sheets into intimate contact with the articles to be decorated.
Typically, the temperature desired to effect sublimation printing is between about 180 degrees C. and 215 degrees C., depending on the inks and colors utilized, and the pressure must be sufficient to ensure a direct touch between the plates and the articles.
Many manufactured articles require labeling on exterior surfaces for environmental, aesthetic, identification or safety reasons. As a rule the exterior surfaces do not lend themselves to printing of indicia which is visually distinct and easily recognizable. As an example, most composite articles have optically dark surfaces due to coloration of the resin and fiber mixtures. Thus, when imprinted with designs or indicia, the resultant image is difficult, if not nearly impossible, to see.
One approach to this problem has been suggested by U.S. Pat. No. 6,004,900 to O'Brien, III. In that patent, the inventor discloses an article made of “unconventional” composite materials and a method of manufacture of the article, in which the article carries an image applied through a sublimation printing process. The patentee describes, as the state of the art, the manufacture of composite articles having an outermost surface that provides an optically light color for application of visually distinct sublimation print, as a process that consists of the steps of forming the article from “conventional” composite materials, coating the surface of the article with an “unconventional” optically light surface ready for application of visually-distinct sublimation print, and sublimation printing on the optically light surface.
In contrast, the composite article of the patent is manufactured by incorporating into the resin mixture an optically-light coloration additive, such as titanium dioxide, which following curing of the article, renders the surfaces of the article ready for application of visually distinct sublimation print.
In another approach, U.S. Pat. No. 5,811,371 to Egashira et al. discloses an article made of materials other than composite materials which includes a first “image receiving sheet” comprising a base sheet and a second receiving layer for receiving a dye or pigment applied through a sublimation printing process, where the receiving layer contains a white pigment, specifically a pigment such as titanium dioxide.
Thus, it appears that evolution of this technology, i.e., the science of applying an image to otherwise optically dark surfaces of an article comprised of composite materials via sublimation printing techniques, has moved in the direction of adding a whitening agent to the uncured resin used in forming the composite article, thereby altering the optical properties of the outer surface of the article on which an optically-distinct image is to be applied after curing of the article.
In contrast, and against this background of known similar technology, the applicant has developed a novel article made of composite materials and resin, as mentioned above, and a method for fabricating the article, in which an optically-distinct image is “applied” to the article prior to curing and remains optically-distinct, after curing of the article, against the ordinarily optically dark coloration of a cured conventional, non-optically enhanced, resin.
More specifically, the invention encompasses an article formed from composite material, including conventional fibrous material and conventional resin material, which, after curing, includes one or more regions exhibiting an image which had been applied prior to curing to the one or more regions in the stack of uncured composite layers, through a sublimation printing process.